A semiconductor fabrication line performs various processing steps to wafer substrates to produce integrated circuits. Present fab systems use reticle or full wafer masks which are stored in standard mechanical interface (SMIF) pods, front opening unified pods (FOUPs), or stocked as bare masks. Wafer sizes vary depending on the semiconductor process; typical maximum sizes are 200 mm and 300 mm in diameter. Wafers can be stored in SMIF pods or FOUPs, which hold as many as 25 substrates.
Intermediate term stocking and short term buffering of substrate carriers is needed to supply the articles to the manufacturing steps as needed. To address the high throughput demands of many manufacturing environments a stocking/buffering system is needed to store carriers in quantity and transfer it via an automated method. The system is either placed in a stand-alone mode where its purpose is to feed material to the Fab itself or in a local mode where it feeds a local tool or tool cluster.
Presently, the main design technique in building these systems automation components is the use of Cartesian slide systems configured in such a way as to achieve the desired motion profile through a plurality of degrees of freedom, usually 3 or 4. The automation components are a combination of linear positioning stages and other motion systems.
One of the major problems of this method has been the automation component itself. Usually being an aggregation of several linear slides, the reliability and serviceability of such systems have been consistently poor. Linear slide systems are subject to alignment problems, which can cause binding and malfunction resulting in a low mean-time-between-failure performance. Also since this is not a true unified automated solution, the design, assembly, and programming time is greatly increased.
Another method of automation utilized is a selective or single compliant assembly robot arm (SCARA) robot mounted on an extra vertical axis of motion to achieve a specific Z height. Although this method is much more reliable than the Cartesian system, the SCARA robot needs a very large footprint to negotiate the product through. This in many cases, results in a system that is unacceptable in size to end users where applications are space critical.
The prior art stocking systems do not have the capability of selecting a carrier from a stocking area and transferring it directly to front end automation with multiple load ports.
A need exists for a method and apparatus for stocking substrate carriers that is small in footprint, highly reliable, and easy to service.